We can readily comprehend the division of time into days and nights, for these, as we have said, are the natural divisions. Let us trace the origin of more arbitrary periods, such as hours, and weeks, and months, and years. First, then, as to days, let it be remembered that the beginning and ending of an ordinary English day differs in several respects from those of other nations. The Jews reckon their day, as do also the Greeks and Italians, from sunset to sunset; the Persians from sunrise to sunrise. The astronomical and nautical day is computed from noon to noon, and is reckoned by 24 hours, not by twice 12,--as, for instance, instead of writing half-past four in the morning of, we will say, Jan. 2, the astronomer would write Jan. 1. 16 h. 30 m. Our ordinary English day is reckoned from 12 to 12 at midnight, after the fashion set by Ptolemy, which has this advantage over the method of reckoning from sunrise or sunset, that the latter periods are continually varying with the seasons of the year. The grouping of seven days into a week is shown in Genesis, but the seventh day is there alone specially named. The Sabbath is still kept by the Jews on the seventh day, but Christians keep the first day of the week in honour of Christ's resurrection, and call it the Lord's Day. After the older planetary method, Sunday was named in honour of the Sun, Monday of the Moon, Tuesday of Tuesco, or Mars, Wednesday of Woden or Mercury, Thursday of Thor, Friday of Friga, Venus, Saturday of Saturn. The Month, named after the Moon in consequence of a month being nearly equal to the time occupied by the Moon in going through all her changes, is again classed under the names lunar or calendar; the lunar month is rather more than 29-1/2 days, but as the solar month is nearly a day longer it would require more than twelve lunar months to make a year, arbitrary additions have been therefore made to each month, some consisting of 30, some of 31 days; and months so arranged to form the calendar are called calendar months, twelve of which make a year of about 365-1/4 days. Until the time of Julius Cæsar the year was reckoned as of 365 days only, a number which after many centuries required the addition of ninety days to rectify, he therefore ordered one of the years to consist of 444 days, and that subsequently every fourth year should contain 366 days. Even this very summary imperial method was attended with its drawbacks and difficulties, for the earth's revolution round the Sun is made in eleven minutes eleven seconds, less than 365-1/4 days, which minutes in the course of about 1600 years required to be taken into consideration, and in 1582 Pope Gregory XIII. took off ten days by making the 5th of October the 15th; but the Gregorian time was not introduced into England till 1752 when the error amounted to about eleven, so eleven days were subtracted from 1752 leaving it only 354 days,--much to the indignation of the